This invention relates to the focusing of beams of light on small targets.
There are many applications in which it is desired to direct light on a relatively small target with substantial uniformity over a wide range of solid angles. An example of such a use is afforded to efforts to couple light from high-power laser beams to light a fusion reaction in a small pellet. Various approaches have been taken to meet the objectives described above. One is to use a plurality of beam splitters to split the beam into many beams and then to reflect the many beams at the target from different angles. This has the disadvantage of requiring one illumination aperture at the target for each of the split beams. Design of such a system is complicated further if it is desired to make such a system respond to a relatively wide light spectrum. Such a system is normally referred to as achromatic when it is capable of focusing light with relatively uniform focus over a range of wavelengths that exceeds 0.2 microns. In general, systems for such focus that employs a number of lenses are narrow band systems because of the difficulty of correcting refracting optical elements over a range of wavelengths.
Where the objective of the designer is to deliver light to a target as for fusion, it will usually be necessary to introduce the light through a relatively small aperture that is capable of withstanding a vacuum. This makes it desirable to have a minimum number of apertures, since each such aperture may comprise a vacuum port.
It is an object of the present invention to provide a system for delivering light to a small target over a wide range of solid angles.
It is a further object of the present invention to provide an apparatus for illuminating a small target by light admitted through a small number of apertures.
It is a further object of the present invention to provide a system that delivers light to a small target with substantial uniformity over a wide range of light frequencies.
Other objects will become apparent in the course of a detailed description of the invention.